Nuclear techniques at ANSTO have helped to confirm a quantum spin
phenomena, a Haldane phase, in a magnetic material, that has potential
to be used as a measurement model for quantum computation.

Although there has been experimental evidence of the Haldane phase
in other types of one dimensional antiferromagnetic materials, it is
believed to be the first evidence in a cluster-based material.

The neutron spectrum from Pelican provided the very data that
confirmed Haldane state exists in fedotovite as proposed by our other
measurements and theoretical studies. The neutron data showed both spin
gap and dispersion, that are characteristics of the Haldane state, said
lead author A/Prof Masayoshi Fujihara of the Tokyo University of
Science.

In an article published in Physical Review Letters as an
'Editors Suggestion' , a large collaboration of researchers,
led by physicists from Japan, ANSTO instrument scientists Drs Richard
Mole, Dehong Yu and Shinichiro Yano of the National Synchrotron
Radiation Research Centre in Taiwan (who operates the Taiwanese
instrument Sika at ANSTO), shared experimental evidence of the Haldane
phase in fedotovite.

The framework for this unusual state of matter was predicted by
Prof Duncan Haldane, who shared the Nobel Prize in Physics for the
development of the topological phases of matter theory with David
Thouless and Michael Kosterlitz in 2016.

Quasi one dimensional spin systems, such as fedotovite K2Cu3O
(SO4)3, have an unusual magnetic behaviour at very low temperature, in
which the ground state is a one-dimensional chain in a triplet
configuration with S=1 spin. The S=1 occurs because there are an even
number of S=1/2 on the magnetic Cu2+ ions at the ends of spin chain, as
predicted by Haldane. Quasi-one dimensional chains such as fedotovite do
not have a single spin but a group of spins forming a cluster. One
cluster of atoms then weakly interacts with the neighbouring cluster of
atoms, said Mole.

Magnetic coupling occurs because of super exchange interactions
between the spin clusters and small antiferromagnetic coupling within
the cluster.

That gapped behaviour is observable in the Pelican spectrum, which
is highly sensitive to weak magnetic interactions, said Mole.